USB devices and smartmontools
To access USB storage devices, the operating system sends SCSI commands through the USB transport to the device. If the USB device is actually a PATA or SATA disk in an USB enclosure, the firmware of its USB bridge chip translates these commands into the corresponding ATA commands. This works straightforward for read and write commands, but not for SMART commands.
To access SMART functionality, smartmontools must be able to send ATA commands directly to the disk. For USB devices, at least the following conditions must be met:
- The USB bridge provides an ATA pass-through command.
- This command is supported by smartmontools.
- The operating system provides a SCSI pass-through I/O-control which works through its USB-layer.
- SCSI support is implemented in the operating system interface of smartmontools.
Some recent USB bridges already support the vendor independent SAT (SCSI/ATA Translation, ANSI INCITS 431-2007) standard. Other USB bridges provide vendor specific ATA pass-through commands. The current version of smartmontools supports the following pass-through commands and USB bridges:
|Command||USB bridges||smartctl option||48-bit ATA support||Comment|
|SAT ATA pass-through 12 and 16||various (ASMedia, Initio, Oxford, newer JMicron, ...)||-d sat[,16]; -d sat,12||requires '-d sat[,16]'||Older Linux kernels may require '-d sat,12'|
|Cypress ATACB||Cypress CY7C68300B/C (AT2LP), CY7C68310 (ISD-300LP)||-d usbcypress[,CMD]||No||CY7C68300A (AT2) may not work.|
|JMicron ATA pass-through||JMicron JM20329, JM20335-39, Prolific PL2507/3507||-d usbjmicron[,p][,x][,PORT]||Yes (SATA only)||'-d usbjmicron,x' enables 48-bit support|
|Prolific ATA pass-through||Prolific PL2571/2771/2773/2775||-d usbprolific||Yes|
|Sunplus ATA pass-through||Sunplus SPIF215/6, SPIF225/6||-d usbsunplus||Yes|
Smartmontools was successfully tested with many USB devices on several Platforms. If the USB ID can be obtained from the operating system, smartmontools also supports auto-detection of (the already tested) USB devices. Then it is not necessary to specify the '-d' option. See the following table for details:
|Platform||...has SCSI pass-through||smartmontools supports SCSI||... supports USB||... auto-detection||... in smartd DEVICESCAN||Comment|
|Linux||Yes||Yes||YES||YES||YES||See comment about SAT in above table|
|Mac OS X||No||No||(Yes)||(Yes)||(Yes)||via OS-X-SAT-SMART-Driver, see below|
The OS-X-SAT-SMART-Driver provides access to SMART data for SAT capable USB and Firewire devices on Mac OS X. This works without -d sat option. Note that this does not support USB bridges with vendor specific commands (JMicron, Sunplus), 48-bit ATA commands (-l xerror) or non-SMART ATA commands (-s apm,N). Full USB support would require SCSI pass-through support which does not yet exist on Mac OS X.